IEEE Standards - Draft Standard Template s2

IEEE C62.42/D1, October 2007

IEEE PC62.42™/D1
Draft Guide for the Application of Component Surge-Protective Devices for Use in Low-Voltage [Equal to Or Less Than 1000 V (ac) Or 1200 V (dc)] Circuits

Prepared by the 3.6.3 Working Group of the
Surge Protective Devices Committee

Copyright © 2007 by the Institute of Electrical and Electronics Engineers, Inc.
Three Park Avenue
New York, New York 10016-5997, USA
All rights reserved.

This document is an unapproved draft of a proposed IEEE Standard. As such, this document is subject to change. USE AT YOUR OWN RISK! Because this is an unapproved draft, this document must not be utilized for any conformance/compliance purposes. Permission is hereby granted for IEEE Standards Committee participants to reproduce this document for purposes of IEEE standardization activities only. Prior to submitting this document to another standards development organization for standardization activities, permission must first be obtained from the Manager, Standards Licensing and Contracts, IEEE Standards Activities Department. Other entities seeking permission to reproduce this document, in whole or in part, must obtain permission from the Manager, Standards Licensing and Contracts, IEEE Standards Activities Department.

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Introduction

(This introduction is not part of IEEE PC62.42/D1, Draft Guide for the Application of Component Surge-Protective Devices for Use in Low-Voltage [Equal to Or Less Than 1000 V (ac) Or 1200 V (dc)] Circuits.)

Patents

Attention is called to the possibility that implementation of this guide may require use of subject matter covered by patent rights. By publication of this guide, no position is taken with respect to the existence or validity of any patent rights in connection therewith. The IEEE shall not be responsible for identifying patents or patent applications for which a license may be required to implement an IEEE standard or for conducting inquiries into the legal validity or scope of those patents that are brought to its attention.

Participants

At the time this draft guide was completed, the 3.6.3 Working Group had the following membership:

Tom Hartman, Chair

Bill Travis, Vice-chair

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This is an unapproved IEEE Standards Draft, subject to change.

IEEE C62.42/D1, October 2007

Participant1

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This is an unapproved IEEE Standards Draft, subject to change.

IEEE PC62.42/D1, October 2007

The following members of the balloting committee voted on this guide. Balloters may have voted for approval, disapproval, or abstention.

(to be supplied by IEEE)

CONTENTS

This is an unapproved IEEE Standards Draft, subject to change.

IEEE PC62.42/D1, October 2007

Draft Guide for the Application of Component Surge-Protective Devices for Use in Low-Voltage [Equal to Or Less Than 1000 V (ac) Or 1200 V (dc)] Circuits

1. Overview

1.1 Scope

This guide covers the application of air gap, gas tube, metal oxide varistor, and avalanche junction semiconductor components used in surge protective devices, equipment, or systems involving low-voltage power, data, communications and signaling circuits. This guide is intended to be used with, or to complement, related documents IEEE C62.31, C62.32, C62.33 and C62.35.

1.2 Purpose

The purpose of this guide is to provide manufacturers, designers and users of low-voltage power, data, communication and signaling circuits with component surge protective device applications and the interaction and coordination of two or more components surge protective devices.

1.3 How to use this document

Explain clause contents Add clause for environmental threat and application considerations

2. Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments or corrigenda) applies.

IEEE Std C62.31™-2006, IEEE Standard Test Methods for Low-Voltage Gas-Tube Surge-Protective Device Components

IEEE Std C62.32™-2004, IEEE Standard Test Methods for Low-Voltage Air Gap Surge-Protective Device Components (Excluding Valve and Expulsion Types)

IEEE Std C62.33™-1982 (Reaff 1994), IEEE standard test specifications for varistor surge-protective devices

IEEE Std C62.35™-1987, IEEE standard test specifications for avalanche junction semiconductor surge protective devices

3. Definitions

For the purposes of this draft guide, the following terms and definitions apply. The Authoritative Dictionary of IEEE Standards, Seventh Edition, should be referenced for terms not defined in this clause.

3.surge protective component, SPC: Constitutes part of a surge protective device which cannot be physically divided into smaller parts without losing its protective function

NOTE—The protective function is non-linear, amplitude restriction effectively begins when the amplitude attempts to exceed the predetermined threshold value of the component.

[ITU-T K.65, MOD IEV 151-11-21]

3.modes of protection (of an SPD or voltage limiting network): terminal-pairs where the diverted surge current is directly between that terminal-pair without flowing via other terminals

3.Antenna-coupling component: component connected from an accessible metal part to a nominal 125 V or 250 V line circuit within an appliance.

[MOD UL 1414]

3.Class Y1 component: component connected from an accessible metal part to a nominal 250 V line circuit within equipment.

[MOD UL 1414]

3.Class Y2 component: component connected from an accessible metal part to a nominal 125 V line circuit within double insulated equipment, or a component that is connected from an accessible metal part to a nominal 250 V line circuit within grounded equipment.

[MOD UL 1414]

4. Air Gap

Technology

4.1 Carbon Block Air Gaps

The carbon block is a form of component air gap. Although still installed in many telecommunications systems (Add picture and description) new telecommunications designs use GDTs or some other form of SPC. As a device, rather than a component, quite large numbers are used for AC supply lightning arresters.

4.2 Metallic Air Gaps

BUGs need, Watt-hour meter protection contribution, Antenna use

5. Gas Discharge Tube, GDT

Gas discharge tubes consist of two or more metal electrodes separated by a small gap and held by a ceramic or glass cylinder. The cylinder is filled with a noble gas mixture, which sparks over into a glow discharge and finally an arc condition when sufficient voltage is applied to the electrodes. When a slowly rising voltage across the gap reaches a value determined primarily by the electrode spacing, gas pressure and gas mixture, the turn-on process initiates at the sparkover (breakdown) voltage. Once sparkover occurs, various operating states are possible, depending upon the external circuitry. These states are shown in Figure 1. At currents less than the glow-to-arc transition current, a glow region exists. At low currents in the glow region, the voltage is nearly constant; at high glow currents, some arrester types may enter an abnormal glow region in which the voltage increases. Beyond this abnormal glow region the tube impedance decreases in the transition region into the low-voltage arc condition. The arc-to-glow transition current may be lower than the glow-to-arc transition. The GDT electrical characteristic, in conjunction with the external circuitry, determines the ability of the gas tube arrester to extinguish after passage of a surge, and also determines the energy dissipated in the arrester during the surge.

If the applied voltage (e.g. transient) rises rapidly, the time taken for the ionization/arc formation process may allow the transient voltage to exceed the value required for breakdown in the previous paragraph. This voltage is defined as the impulse breakdown voltage and is generally a positive function of the rate-of-rise of the applied voltage (transient).

A single chamber three-electrode GDT has two cavities separated by a centre ring electrode. The hole in the centre electrode allows gas plasma from a conducting cavity to initiate conduction in the other cavity, even though the other cavity voltage may be below the sparkover voltage.

Because of their switching action and rugged construction, gas tubes exceed other SPD components in current-carrying capability. Many telecommunications gas tubes can easily carry surge currents as high as 10kA, 8/20, depending on design and size values currents of >100kA can be achieved.

The construction of gas discharge tubes is such that they have very low capacitance, generally less than 2 pF. This allows their use in many high-frequency circuit applications.

When GDTs (gas discharge tubes) operate, they may generate high-frequency radiation, which can influence sensitive electronics. It is therefore wise to place GDT circuits at a certain distance from the electronics. The distance depends on the sensitivity of the electronics and how well the electronics are shielded. Another method to avoid the effect is to place the GDT in a shielded enclosure.

Figure 1 —Typical GDT voltampere characteristic

5.1 GDT Key Parameters

In terms of voltage limiting performance a GDT has four key parameters; sparkover voltage, glow voltage, arc voltage and DC holdover voltage.

5.1.1 GDT sparkover voltage

5.1.1.1 DC and impulse sparkover voltage

The maximum value of limited voltage depends on the surge voltage rate of rise. Figure 2 shows a typical relationship between the GDT DC sparkover and the impulse, fast rate of voltage rise, sparkover of a GDT. In this example, the minimum 1000V/µs sparkover voltage of 575V occurs with a 150V DC sparkover voltage GDT. The much lower voltage 75V DC sparkover GDT has a 1000V/µs sparkover voltage of 700V – nine times higher than the DC value. Where fast rising transients occur, often the 150V GDT will be more effective than a 75V GDT.

Figure 2 —Fast dv/dt sparkover voltage variation with DC sparkover voltage

Figure 2 shows absolute values of voltage. In terms of relative voltage increase, then this factor continuously decreases with increasing voltage, being; 9x at 75V, 4x at 150V, 2.6 at 300V and 2.1 at 600V. For example, two 150V GDTs in series would have a 1000V/µs sparkover of 1150V, but a single 300V GDT would have a 1000V/µs sparkover of 775V. Two or more series connected GDTs will always have a net 1000V/µs sparkover voltage higher than the equivalent single GDT. These numbers are just for demonstration of GDT characteristics and may vary for different designs.

5.1.1.2 Sparkover voltage stability

GDTs have inherent wear out mechanisms, by selecting the appropriate GDT for an application the desired service life can be achieved, such as 30 years for network telecommunications equipment. Prime indicators of wear out are changes to the insulation resistance and sparkover voltage. Figure 3 shows the measured change in sparkover voltage with number of impulses for heavy duty 500A, 10/1000 GDTs. This shows the importance of suppliers giving users assurances of not only day-one performance, but also stability over life.

Designers would like GDTs with DC to impulse sparkover voltage ratios as low as possible, popularly these are called “Fast” GDTs. In 2000, as a response, some manufacturers introduced “Fast” GDT formulations with lower sparkover voltages. The downsides to such formulations where often-higher arc voltages, more AC power loss, and shorter life times compared to standard GDTs. In one European deployment, a maintenance program had to be set up to replace a particular type of “fast” primary GDT every two years.

Because the characteristic of a "Fast" GDT is different, it can form a relaxation oscillator with the rest of the circuit. During laboratory AC power fault testing, the burst of HF oscillation generated when the GDT sparks over often destroys xDSL driver ICs. This is partly due to testing technique, as other connected equipment is decoupled to prevent diversion of the AC power fault current away from the equipment under test. In an actual system the loading from the decoupled equipment may damp out the oscillation tendency.

Figure 3 —350 V GDT DC sparkover voltage variation with repetitive surging

5.1.1.3 Sparkover dark effect

Some GDT data sheets specify that the sparkover measurement is made with the GDT “In ionized mode”. This means that the GDT has gas in a pre-ionized state when the sparkover voltage measurement is done. Just because a manufacturer doesn’t state any preconditions doesn’t mean they don’t test their GDTs in a pre-ionized state.

The “dark effect” is a term that describes the difference between the non-ionized sparkover voltage and the pre-ionized sparkover voltage. A good illustration of the “dark effect” is a telecommunications repeater history. A particular repeater was failing in the field, but laboratory testing showed the repeater had excellent withstand to surges. That is, until one day the testing was done with the repeater box lid on and the repeater failed. What happened was with the lid off, light falling on the GDT pre-ionized the gas filling and resulted in a lowered sparkover voltage. When the lid was in place to a period, there was no gas pre-ionization and a much higher first surge sparkover voltage, damaging the repeater. Further sparkover measurements gave a lowered sparkover voltage, as the gas was pre-ionized from the first surge. This experience gave rise to the “dark effect” term.

GDTs were then introduced with radioactive traces in the gas filling, which pre-ionized the gas. Now radioactive GDTs are banned, the “dark effect” is back. Normally, to test for the dark effect, the GDT is kept in darkness for 24 hours then tested. Some manufacturers build the “dark effect” increase into their quoted sparkover voltages and test to tighter voltage levels in production (as production isn’t done in total darkness). The dark effect can be minimized by the internal geometry of the GDT and the emission coatings used.

5.1.2 GDT glow voltage

The glow voltage region influences two operational areas; DC holdover and low AC power loss. When a GDT is connected to conductors sourcing DC power it is possible for a current limited DC source voltage to maintain the GDT in the glow region after a surge. If the glow voltage is higher than the DC source voltage, then latch up in the glow region cannot occur. In AC power fault conditions, if the current flow is limited to below that need for a glow-to-arc transition, typically 100mA to 1.5 A, depending on design,, the GDT can have a significant power loss in this high-voltage low-current condition.